Pass actual present time to ViewRootImpl

To measure end-to-end touch latency, we need to report the actual
present time to ViewRootImpl. ViewRootImpl, in turn, will report this
information to InputDispatcher. Finally, InputDispatcher will combine
all known information for a specific input event, and will report this
data to westworld.

In another patch, we will add a new call, 'reportLatencyInfo', to
InputPublisher. This call will allow the app to send this latency data
to InputDispatcher.

Bug: 169866723
Test: printed the input event present times inside ViewRootImpl
Change-Id: Ibd3a2cfeb1a340eb15cd2165071df1f8589634af